1. Field of the Invention
The present invention relates to lead-free solders and soldered articles.
2. Description of the Related Art
Solders have been conventionally used for achieving an electrical and mechanical joint to electronic devices and electronic parts. Solders containing tin and lead as major components have been generally used. In addition, solders not containing lead, so called "lead-free solders", which contain tin as a major component and other components such as silver, bismuth, copper, indium and antimony, are being used in consideration of environmental problems. In recent years, soldered articles provided with electrical joints having satisfactory soldering characteristics have been produced using such lead-free solders.
However, solders containing tin as a major component, particularly lead-free solders, readily form electrode erosion at electrical joints during soldering or during thermal aging after soldering. When components readily diffusing into tin are used in compositions of electrodes to be soldered, electrode erosion will be further prompted.
Lead-free solders containing tin and silver as major components also have been proposed; however, hard tin-silver alloys will be further hardened so that plastic deformability is significantly decreased by addition of nickel for the purpose of improved electrode erosion resistance during soldering.